Process for the preparation of borneol esters from turpentine.



J. HERTKORN.

PROCESS FOR THE PREPARATION OF BORNEOL ESTERS FROM TURPENTINE. APPLIOATION FILED JUNE 1, 190B.

. 991,293 Patented Oct. 13,1908.

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vTo'all whom it may concern:

. Be it known that I, J OSEF HERTKOR'N, doctor of philosophy, chemist, and resident of Berlin, German (whose post-office address-is .Paulst'rasse 8,) ave invented a new and use-' ful Improved Process forthe Preparation of Borneol and Isoborneol Esters from Oil of Turpentine, of-which the following. is a specification.

My invention relates to a process for producingborneol and isoborneol esters from I .25 i I for days at this temperature, only very small quantities of the borneol ester are obtained,,

oil of turpentine.

1 It is well known that borneols and their esters can be produ'ced'from oil of turpentinein various ways, as, for instance, by treatment with bOI'lC acld or w1th benzoic acld,

but a serious objection exists to all these known processes on account of the small yield of borneol, which is far less than the theoretical yield. 7 a

' I have found that 'the temperature suitable for .esterification when treating oil of turpentine with anhydrous acids or their anhydrids does not lie between 130 and 132C. as hashitherto been assumed, for after digestion and therefore only very small quantities of camphorcan be produced. Inthis reaction the pinene of the oil of tu entine is probably first converted into-camp one, and this by a secondary action into the borneol esters.

If the esterifying acid, boric acid for example, be mixed with anhydrous oil of turpentine and heated for days; at-a. temperature of from 130 to- 132 0., the same oor yield of borneol esters is obtained. If, however, metaboric acids, and particularly pyroboric acids be employed, that is to say boric acid anhydri-ds, and if at least enough of these acids is added to combine in e uivalent pro ortions to form camphene'triorate, and t e temperature is raised to from 165 to 176 (3., there is obtained in a far shorter time a considerably greater yield, namely from 5 to 10% of borneol esters. 10 .to- 13 an acid is necessary. v 1

As is well known, solid camphene when heated at high temperatures from 130 to 180 (1, forms borneol and isoborneol esters inan: almost theoretical yield, there being prac tically no by-products, but this action only takes place at quite a high temperature. It is also well known that .camphene can be formed in small quantities fromoil of 'tur- Specification of Letters Patent. I Application flled June 1, 1908. Serial no; 435,889. 1

. perature.

, pose.

per cent. of suchcailnphene at from 16.0 to 180 Patented Oct. 13,1908.

pentine by the action of anhydrous acids or similar hydrolyticall 1 acting substances, such as concentrate sulfuric acid, acetic acid, and the like.

The chemical'reaction in the above mentioned formation of borneol esters from pi- -molecule in thedirection of camphene. Pi-

nene molecules can be rearranged either in the direction of camphene or in the direction of limonene,--or these two substances can be formed conourrentl according to the kind of acid, the method Limonene is not adapted for the direct formation of borneol and is consequently a troublesome by-product. The yield of borneol esters is therefore dependent wholly upon the uantity of the camphene formed.

It is we known that pinene whenheated most entirely changed into limonene, and

of working, or the hy- I drolytically acting additions.

with free acids to from 120 to 130 0. is althat therefore only very little ca'mphene is produced. The quantity of limonene is the greater the stronger the acid, the longer the heating is kept up, and the higher the tem- At the temperature mentioned above, the small quantity of campheneformed is only very incompletely converted into borneol esters, since a temperature of from 160 to 180 C. is necessary for thispur- In the-ordinary process, the formation of camphene is practicallyentirely precluded at this high temperature because the formation of limonene increases rapidly at anything above 132 C. The chemical rea ction considered, generally presents two malnphases v 1. The formation of camphene at about from 120 to 140 centigradeand 2. The formation of the borneol ester from centigrade. ave discovered by further experiments that the formation of limonene can be partially or entirely stop ed, resulting 1n an increased production 0 camphene, by the use of protective substances, such as anhydrous alcohols, phenols, or their derivatlves and materials acting like alcohols and phenols, such as glycerin. The neutral or acid esters of the reaction.

are especially valuable for the purpose of yielding such protective substances. In fact, any esters which will break down at from 120 to 140 C. (the camphene forming temperature) or'at a higher temperature, into acid esters or into free acids wlthout splitting ofi water, are articularly adapted for this purpose. Sue decomposable esters yield acid radicals which become readily combined with the camphene as it forms, protecting the be distilled off, mix with the water formed by the principal reaction and the subsidiary reactions and immediately carry such water off innocuously.

Preferably the esterification acids and the hydrolytically acting added substances must be partially or wholly alreadycombined with the protective substances before they are added to the oil of turpentine, so that the pinene does not come in direct contact in the first stage of the operation with the free acid, as this would aid the formation of limonene in a high degree. The protective substances act simultaneously as acid-binding, acid-diluting, acid-distributing, and acid-dissolving agents, when the esterification acid or the ester roduced is soluble with difficulty or insolub e in-oil of turpentine. Examples of such esterification acids are the metaand pyroboric acids, hosphoric acid, arsenic acid, oxalic acid, actic acid, cumaric acid, cresotinic acid, salicylic acid, benzoic acid,

tartaric and citric acids, succinic acid, oxyna hthoic acid, phthalic acid, gallic acid or 0t 161 monoor polybasic weak organic or in. organic acids or oxyacids or their derivatives.

According to my invention, the protective substances or their readily decomposable esters prevent the formation of limonene either wholly or artially and thereby aid, to a high degree, the formation of camphene and of borneol esters. The introduction, even in small proportions and at wide intervals of time, of the esterification acid diluted with a protective substance into the oil of turpentine, which preferably has been previously diluted with a protective substance, causes a materially better yield (20 to 25%) of borneol ester. a

My experiments have shown that the greatest ield that is about 70% of borneol esters is 0 tained by the use, as readily decomposable esters heretofore referred to, of weak -polyvalent inorganic or organic acids, which are capable of easily forming acid esters and which at high temperatures again split up, partially or wholly and without profound decomposition, into protective substances and acids. As such decomposable esters,

preferably only those substances are used which do not on decomposition yield water, and which in addition are easily soluble in water or in alkaline solutions, the protective substance of which is easily volatile, and the terpene esters of which are easily decomposed by water 'or alkaline solutions for the easy separation and recovery borneol and the by-products.

The esters of the protective substances may be formed separately and added to the oil of turpentine or to the mixture ofoil of turpentine and acid. As an alternative esters maybe led as gases into the oil of turpentine, or into the mixture of oil of turboiling point of the oil of turpentine or of the acid used. 1

In the accompanying drawing which shows in cross section an apparatus for carrying out my invention, A represents an oil vided with a thermometer K. Mounted tends over the top of the digester vessel and the oilbath a'nd'is bolted thereto, washers being used if desired to make tight joints. The cover 0 is provided with a stuffing box D'through which projects a'stirr'er 0 provided with any desired form of stirring blades. man hole op'eningM, a thermometer J, and a tube V for introducing vaporized alcohol into the vessel B.

v N represents a discharge tube for the vaporized materials and it delivers into either one or the other of the two Liebig condensers R and R a three-way cock P being'probe directed either into the condenser R or the condenser R as desired. The condenser R, is used as a reflux cooler, while the condenser R is directed downwardly for the Mounted on the top of the cover 0 is a bent bracket H, and through a bearing in the shaft of the stirrer passes, which shaft is provided with a bevel gear wheel E which meshes with a similar wheel F on a'horizontal bracket H, and which shaft is provided with a driving pulley G. The oil bath may be heated by a gas lamp or in any desired way, and instead of the oil bath a closed steam boiler might beemployed.

Example 1. Into the vessel B are fed 150 kilos of anhydrous rectified oil of turpentine,

kilos of absolute alcohol or methyl alcohol, and from 20 to '30'kilos' of finely powdered so as to connect the pipe N with the pipe in thereof from the I method, the protective substances or their pentine and acid at a temperature below the within the oil bath is the digesting vessel B having a rim at its upper end extending over the top of the oil bath A. A cover 0 exbath supported on legs L and L and pro- The cover is also provided with a vided, so that the volatilized materials may 1'10 discharge of the materials condensed therein.

u per horizontal portion of this bracket tli shaftmounted in the vertical part of the boric acid anhydrid. The cock P is turned the interior of the reflux condenser R,, the stirring, apparatus is set in motion and. the oil bathAheated. This heating and stirring, with the reflux cooling arrangement, is continued for about 12 hours at about from 70 to 100 C., until the alcohol has become esterified with the acid. The cock -P is then turned to connect the pipe N with the condenser R, and the uncombined alcohol and the water roduced in the previous boiling are then dlstilled off at from 70 to 90 C. The cock P is then turned'to connect the apparatus with the reflux condenser R and the mixture in the vessel B is boiled under a slowly increasing heat until the temperature reaches about 115 C.,this operation taking about an hour. The cock P is then turned to connect the pipe N with the condenser R and then the temperature in the vessel B is raised progressively and slowly from 115 up to about 135 C., this operation consuming about twelve hours, during which time the water produced by the various reactiors is distilled ofi togetherwith any alcohol in the vessel B and with the volatile and neutral alkyl borate, and when this distillation. is complete the boiling point of the material in the vessel B rises. The neutral a-lkyl borate is thus decomposed, first, into the acid ester and alcohol in the presence of the unchanged neutral borate; and, at a later phase, partially into free acidand free alcohol. The material in the vessel B is then heated for about twelve hours, the temperature being slowly raised from 135 C. to about 160 C., whereby the last portions of the volatile alkyl ester and the alcohol which has been set free are slowly distilled ofi. The acid borate first converts the pin'ene into camphene by rearrangement, and the carnphene becomes converted by the acid of the ester, or, the boric acid which has been setfree, into the borneol ester, which can be recognized by the increasing viscosity of the liquid. When the mass has become viscous, it is heated for about six hours at from 160 to 176 C., whereu on the last portions, includmg about 3 ki ograms of alkyl ester with terpenes and alkylenes'and traces of water distil ofi. There remains in the vessel amixture of the boric acid ester of borneol and isoborneol in the form of a reddish brown,

transparent and solid jelly, which liquefies' again between 100 and 150 C. and is easily broken up in the air, or with water, into the hydrates of borneol and boric acid. Above 180 C., the raw borneol borates which usually still contain free boric acid, decompose lntowater and viscous jellies, which yield practlcally no camphor on oxidation. It is of the highest importance, therefore, that the temperature should not be allowed to rise as high as 180 C.

The yield of borneol is increased if the last portlons of the free boric acid are removed kilos of ethyl borate.

from the mixture, and this can be done by boiling the mixture for several hours at from 170 to 176 C., and at the same time-passing a current of absolute alcohol through said mixture.

The operation is materially shortened if instead of the alcohols and acids, the equivalent quantity of neutral or acid ester of these acids be used withor without the addition of some absolute alcohol or free acid, the latter forming with the neutral ester the desired acid ester.

Example 2. The heating of the substances mentioned in the foregoing example may be carried out in an autoclave or digester provided with stirring and distilling-off appliances. After the stirring apparatus has been started, the digester is heated at about 100 C. for about five hours at a pressure of from 5 to 7 atmospheres above that of the atmosphere, or even at a greater pressure. The pressure is then released, and the uncombined alcohol'and water produced in the reaction are distilled off at 115 C. The heating is then continued at about 115 to 125 C. under a pressure of from 5 to 7 atmospheres, and from time to timea certain amount of liquid is blown off in the form of Vapor, the heat being gradually raised until the temperature reaches about 135 C.

This takes from 6 to 8 hours. The digester ucts are distilled oil, until t e boiling point of the liquid rises to about 160 C. The fur-- ther treatment is the same as in the first example.

Example 3. Into a digester such as is described in Example 2, are fed 150 kilos of dehydrated'and rectified oil of turpentine, 50 kilos of absolute alcohol, from 10 to 13 kilos of boric acid anhydrid, and from 50 to 80 Instead of the borate of ethyl the oxalate, lactate, silicate, salicylate, citrate, tartrate, gallate, naphthoate,

cresotinate, acetate, benzoate, or phosphate of ethyl may be used. The digester is then heated to about C. from 10 to 12 hours at an internal pressure of from 7 to 10 atmospheres above that of the atmosphere, the stirring apparatus being set in motion. The pressure is then reduced and the products are distilled off up to a temperature of 140 C. The digester is then a ain heated'at a temperature of 140 to 16 C. from 5 to 6 hours at a pressure of from 5 to 7 atmospheres above the pressure of the atmosphere,

during which time, at intervals, according to the nature and behavior of the particular ester, a small percentage of distlllate is blown off for the purpose of removing the injuriously acting su sidiary product of the reaction and increasing the boiling point. The

l digester is again heated slowly under a reflux condenser at ordinary pressure up to 176 C. as in Example 1.

Example 4. A charge of turpentine, absolute alcohol, and boric acid anhydrid as men tioned in Example 1, having been introduced into the digester, and the mixture heated to from to 0., the vapor of from 100 to 150 kilos of absolute alcohol or methyl alcohol is introduced into the digester. The water roduced by the reaction is distilled off wit the uncombined alcohol continuously. The further treatment may be effected as in Example 1 or Example 2.

The alkyl ester distillates and alcohols obtained in the various examples may be used over again after being dehydrated. The use of the already formed neutrall l or acid esters in place of the ester compo ants, and the carrying on of the operation under'a pressure of from 5 to 10 atmospheres and the formation of the alkyl ester above the boiling point of its components, shortens the operation considerably, and yields a considerably larger output of borneol ester.

The raw borneol esters obtained as dewhile the raw borneols are separated out and removed. These borneols are then purified by the well known method of fractional steam distillation, or by progressively cooling down and fractionating out in supersaturated solutions.

I claim 1. The process of preparing borneol esters,

which consists in heating a mixture of oil of which consists in mlxing oil of tur entine with alcohol and boric acid anhydrid, eating the same until the alcohol has become esterified, distilling off the water and uncombined alcohol, slowly heating up to about 0., and allowing the volatile products to escape, finally heating the mass up to 176 C. and urifying the residual product containing borneol esters, substantially as described.

In testimony, that I- claim the foregoing as my invention, I have signed my name in presence of two witnesses, this nineteenth day of May 1908.

JOSEF HERTKORN. Witnesses:

HENRY HASPER,

WOLDEMAR HAUPT. 

